Many injectable medications and pharmaceutical preparations are distributed to the end user in prefilled hypodermic syringes. This unit dosage form is quick to use, has a high degree of sterility and allows easy control of the dose being administered.
It is very important that the fluid fill of these prepackaged materials be closely controlled -- usually to within a percent or two -- to assure proper dosing. With nonviscous fluids such as dilute solutions in water, this is often not a major problem, and the filling can be carried out automatically with a minimum of supervision and inspection. With viscous fluids there is often an air gap between the face of the syringe plunger and the face of the fluid itself as the fluid is added. This gap can be as much as 0.2-0.4 cc so that if the total fluid fill is in the range of a few cc's or less this gap can introduce a substantial error. This makes it necessary to visually monitor the actual position of the face of the fluid itself so as to be sure that the desired fill level is correctly achieved
One way to indicate the desired fill level is to have it engraved or printed directly on the syringe barrel. This practice was prevalent with reusable glass syringes. It has fallen into some disfavor with many suppliers of prepackaged pharmaceutical preparations which employ substantial amounts of labeling information directly on the syringe body. Unmarked syringes (i.e., a syringe that has not been engraved or printed) have been created to allow the manufacturer flexibility in usage of the syringes for different products with different labeling. In addition, the labeling does not necessarily contain any indication of fill level and may be applied after filling of the unmarked syringe.
Thus, an apparatus is called for to quickly provide an accurate fill-level indication on unmarked syringe barrels. It is such an apparatus and a method for its use that the present invention provides.